This is exactly right. I had two sets of 650s before the present one and sold them both because I couldn't come to terms with the harsh treble, which was so different to what I'd been led to expect. This time I was determined to persevere, and finally, finally, after about 150 hours burn-in, the 650 is starting to sound like all the descriptions of it I've ever read (many of which don't even mention burn-in). Forget about, "I just got it out of the box and it sounds wonderful!" It doesn't sound wonderful out of the box or for a long time afterwards; it sounds harsh and jangly, with a distinctly forward upper midrange. This puppy needs every bit of burn-in the AKG 701 needs, and that should be made clear by anyone recommending it.

Haha, I thought there was special audio that users were passing through the headphones. Thanks for the tip.

some people use white or pink noise, which hits all the sonic frequencies, to burn in their headphones. i'm not really sure that is necessary and can report that all of my headphones have successfully burned in playing regular music.

This is exactly right. I had two sets of 650s before the present one and sold them both because I couldn't come to terms with the harsh treble, which was so different to what I'd been led to expect. This time I was determined to persevere, and finally, finally, after about 150 hours burn-in, the 650 is starting to sound like all the descriptions of it I've ever read (many of which don't even mention burn-in). Forget about, "I just got it out of the box and it sounds wonderful!" It doesn't sound wonderful out of the box or for a long time afterwards; it sounds harsh and jangly, with a distinctly forward upper midrange. This puppy needs every bit of burn-in the AKG 701 needs, and that should be made clear by anyone recommending it.

Are you sure we're talking about the same headphones here? The 650s? There is nothing resembling the Senn sound, be they outta the box or 500 hrs in use, in your comment. I understand people hear things differently, but that's bizarrely different. What source and amp are you using? Even with thinking that may be the reason, it still makes no sense.

I was never a believer in burn-ins. Whatever has caps in them, or even headphones to a certain degree might actually be able to benefit from initial "stress period", perhaps. As far as my personal experience goes, however, I tend to associate the effects to be largely due to the psychoacoustical process of our brain getting used to the new sound we have not previously been exposed to much, possibly with a fair bit of good old placebo effect. There are times when I felt a bit more comfortable after using a new equipment a few times, but never to the point where a hate turns into love and vice versa. Dunno, maybe that just goes out to show I have been buying used gear more often than new ones (well, even then the buyers often claim their stuff is "like new", could use some burn-in and such...)

This is exactly right. I had two sets of 650s before the present one and sold them both because I couldn't come to terms with the harsh treble, which was so different to what I'd been led to expect. This time I was determined to persevere, and finally, finally, after about 150 hours burn-in, the 650 is starting to sound like all the descriptions of it I've ever read (many of which don't even mention burn-in). Forget about, "I just got it out of the box and it sounds wonderful!" It doesn't sound wonderful out of the box or for a long time afterwards; it sounds harsh and jangly, with a distinctly forward upper midrange. This puppy needs every bit of burn-in the AKG 701 needs, and that should be made clear by anyone recommending it.

I was never a believer in burn-ins. Whatever has caps in them, or even headphones to a certain degree might actually be able to benefit from initial "stress period", perhaps. As far as my personal experience goes, however, I tend to associate the effects to be largely due to the psychoacoustical process of our brain getting used to the new sound we have not previously been exposed to much, possibly with a fair bit of good old placebo effect. There are times when I felt a bit more comfortable after using a new equipment a few times, but never to the point where a hate turns into love and vice versa. Dunno, maybe that just goes out to show I have been buying used gear more often than new ones (well, even then the buyers often claim their stuff is "like new", could use some burn-in and such...)

You're entitled to your opinions, like I don't believe people are causing Global Warming, as opposed to it being a natural cyclical temp change that's gone up and down for millennia.

But, how do psychoaoustics account for the fact that "walking away and letting it run for a few hundred hours unattended" makes it sound better when you come back to it?

I have burned-in several amps and headphones, and can clearly hear a big difference much of the time (not always), that has NOTHING to do with becoming acclimated to the sonic or sound signature. The Brain can't adjust to it if you don't listen, except for 2-3 minutes at 50-100 hour intervals.

This is exactly right. I had two sets of 650s before the present one and sold them both because I couldn't come to terms with the harsh treble, which was so different to what I'd been led to expect. This time I was determined to persevere, and finally, finally, after about 150 hours burn-in, the 650 is starting to sound like all the descriptions of it I've ever read (many of which don't even mention burn-in). Forget about, "I just got it out of the box and it sounds wonderful!" It doesn't sound wonderful out of the box or for a long time afterwards; it sounds harsh and jangly, with a distinctly forward upper midrange. This puppy needs every bit of burn-in the AKG 701 needs, and that should be made clear by anyone recommending it.

I have to support Boomana here. If anything, the 650s are bassy out of the box, not trebly and harsh.

You could always test your burn in theory if you had money. Burn in a pair of headphones for a good 300 hours using pink noise or music then listen to a music file. Unplug the headphones and plug in a brand new set and listen to the same music file on the same amp. Do you hear a difference? Only you can say, I don't have the money. All I can say is that my Little Dot has definitely Burned in or I have gotten more used to the sound because it very harsh highs which have now calmed way down into something a lot more harmonic.

This is exactly right. I had two sets of 650s before the present one and sold them both because I couldn't come to terms with the harsh treble, which was so different to what I'd been led to expect. This time I was determined to persevere, and finally, finally, after about 150 hours burn-in, the 650 is starting to sound like all the descriptions of it I've ever read (many of which don't even mention burn-in). Forget about, "I just got it out of the box and it sounds wonderful!" It doesn't sound wonderful out of the box or for a long time afterwards; it sounds harsh and jangly, with a distinctly forward upper midrange. This puppy needs every bit of burn-in the AKG 701 needs, and that should be made clear by anyone recommending it.

I did not hear any change in my HD650 after burn in, I have heard changes in all my other headphones, but most of them is probably in my mind. Most headphons I have had has been harsh in the treble at first (not the HD650), but after burn in or getting used to them it has gone away (not Dt990 ).

some people use white or pink noise, which hits all the sonic frequencies, to burn in their headphones. i'm not really sure that is necessary and can report that all of my headphones have successfully burned in playing regular music.

I wonder if I played Quincy Jones, " The Places You Find Love", for say 100 hours if that would be enough.
Supposedly it utilizes the full audio spectrum.

Are you sure we're talking about the same headphones here? The 650s? There is nothing resembling the Senn sound, be they outta the box or 500 hrs in use, in your comment. I understand people hear things differently, but that's bizarrely different. What source and amp are you using? Even with thinking that may be the reason, it still makes no sense.

Let me give you a bit of history. I've always used Senn phones and owned them all, including 565, 580, 590, 595, 600 and 650. I had the 595 immediately before the 650 and found them fine even straight out of the box. Of course they improved after burn in, but mostly in the bass; treble was acceptable. With the 650s, I could hardly listen, the upper midrange, lower treble was so forward and harsh. The first pair I sold after 10 days, believing burn-in wasn't going to improve them any further. Then I kept reading how mellow and "creamy" they were and wondered if I'd been too hasty. So I bought a second pair, this time a second-hand pair from a deceased estate, possibly not used much as they sounded the same as the new pair. I tried burning them in, probably 60 hours, but after three weeks regular listening still couldn't abide them and sold them. Again after a while of reading Head-Fi and other forums I was persuaded to give the 650s yet another go (Phew!). This time I was determined to burn-them in to blazes and did so, and finally, finally, well after 100 hours, I began to hear what it seems everyone else was hearing...a "mellow" 650. They're still not as mellow as the 595 (brighter treble excepted), but I expect they'll change with more hours.

As to source and amp, I use a venerable Sony 561E CD player into a NAD C320BEE amp. I suspect differences in what we hear has nothing to do with source or amp but choice of music. I listen exclusively to orchestral/classical music. I tend to judge phones on their ability to reproduce massed strings; if there's harshness there it will show up on strings. The 595 was always particularly kind to classical strings (someone recently claimed it has a dip from 1 to 6khz, which, though not showing up on graphs, sounds about right to me), which probably spoiled me for the 650. I cannot offer any more plausible explanation for the disparity in what I and others hear with the 650; I only know that to my ears the 650 is a fairly unforgiving phone that needs a lot of burn-in and decent equipment. After owning three of them and using them with differerent amps I'm quite certain of this, whatever anyone else says.
As to burn-in, I laugh at the suggestion there's no such thing. It's as obvious to me as the sun in the sky.